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EUMETSAT METEOROLOGICAL SATELLITE CONFERENCE15/09/2013 – 20/09/2013, VIENNAEUMETSAT METEOROLOGICAL SATELLITE CONFERENCE15/09/2013 – 20/09/2013, VIENNA
Retrieval of aerosol optical properties for cloudy scenes from METOPM. Grzegorski, R. Lang, G. Poli, A. Holdak and R. Munro
EUMETSAT METEOROLOGICAL SATELLITE CONFERENCE15/09/2013 – 20/09/2013, VIENNA
Overview
• A few words about GOME-2 PMD measurements
• PMAp: Polar Multi-sensor Aerosol product developed at EUMETSAT • AOD over ocean & cloud products operational in Q1
2014• Examples and Verifications
• Work in progress & future plans• First results: AOD over land (PMAp second generation)
EUMETSAT METEOROLOGICAL SATELLITE CONFERENCE15/09/2013 – 20/09/2013, VIENNA
METOP instruments within the project
Instrument
Spatial resolution
Spectral range
comments
GOME Main science channel
80 x 40 km 240nm -800nm, res. 0.25-0.5nm
AAI, bad spatial resolution
Polarization Monitoring Device
10 x 40 km 311nm-803nm, 15 bands
AOD, aerosol type, AAI
AVHRR - 1.08 x 1.08 km 580nm-12500nm, 5 bands
Clouds, scene heterogeneity, desert dust
IASI - 12km (circular) 3700–15500nm, resolution 0.5 cm-1
Coarse mode aerosols (desert dust, volcanic ash)
Auxiliary data
ECMWF wind speed (forecasting)
Temporal interpolation necessary
- Required for retrievals over ocean
surface albedo,Surface elevation
- - Required for land surface retrievals
EUMETSAT METEOROLOGICAL SATELLITE CONFERENCE15/09/2013 – 20/09/2013, VIENNA
The Polarization Monitoring Devices
Band-S No. pix1 pixw. wav1 wav2 1 22 5 311.709 314.207 2 30 4 316.762 318.720 3 37 12 321.389 329.139 4 50 6 330.622 334.443 5 57 6 336.037 340.161 6 84 17 360.703 377.873 7 102 4 380.186 383.753 8 117 19 399.581 428.585 9 138 27 434.083 492.066 10 165 18 494.780 548.756 11 183 2 552.474 556.262 12 187 11 568.070 612.869 13 198 9 617.867 661.893 14 218 4 744.112 768.269 15 224 2 794.080 803.072
• Radiances & stokes fraction
• better spatial resolution
• stokes fraction s = Q/I
EUMETSAT METEOROLOGICAL SATELLITE CONFERENCE15/09/2013 – 20/09/2013, VIENNA
PMAp: AOD retrieval algorithm
• Geometry dependent test with intercomparison of:• calculated
surface signal
• calculated wind speed dependence
• calculated aerosol signal
• Cloud filter:• AVHRR/VIS
• AVHRR/IR
EUMETSAT METEOROLOGICAL SATELLITE CONFERENCE15/09/2013 – 20/09/2013, VIENNA
Best case: Retrieval clear sky & dark surface
• Step 1: A set of AODs (for 8 selected models) and chlorophyll corrections is estimated using three channels: UV [380 nm], VIS/green [520 nm], red edge [800 nm] using least-square minimization. AOD interpolation done at 800nm.
• Step 2: Selection of a aerosol type / chlorophyll / AOD set using least-square minimization of measured and modelled reflectances in all PMD channels. Stokes fractions are used in addition if applicable.
aerosol model number
PM
D
refl
ecta
nce
SZA=40, cos(RAZI)=-1, VZA=45, AOD=4SZA=40, nadir, aerosol model 3
PM
D
refl
ecta
nce
AOD
EUMETSAT METEOROLOGICAL SATELLITE CONFERENCE15/09/2013 – 20/09/2013, VIENNA
Cloud correction by AVHRR
• AVHRR cloud tests:• Albedo test• T4 test• Uniformity test• T4T5 test
• Retrieval for partly cloudy pixels:• Limitation to PMD 13/15• Correct for cloud
reflectance
Channel
Central wave-length[μm]
Wavelength range [μm]
1 0.630 0.580 - 0.680
2 0.865 0.725 - 1.000
3A 1.610 1.580 - 1.640
3B 3.740 3.550 - 3.930
4 10.800 10.300- 11.300
5 12.000 11.500- 12.500
)(
)(AVHRRn
AVHRRnGOMECF
collocated
cloudy
)(
)()()(
~
AVHRRR
AVHRRRPMDPMD
allpixel
clearsky
allcloudfree RR
Geometric cloud fraction:
EUMETSAT METEOROLOGICAL SATELLITE CONFERENCE15/09/2013 – 20/09/2013, VIENNA
Identify pixels misclassified as cloud: Volcanic ash
Orange: Strong ash test positive, cloud tests ignored
Blue: cloud fraction < 0.3, AOD retrieved
White: • no retrieval or • cloud fraction > 0.3
and negative ash test
Aerosol optical depth Volcanic ash flag:
• Brightness temperature difference T4-T5 (10 μm – 12 μm) • Thresholds in VIS and NIR (e.g. AVHRR CH3A/CH2)
EUMETSAT METEOROLOGICAL SATELLITE CONFERENCE15/09/2013 – 20/09/2013, VIENNA
Alternate retrieval combining reflectances & stokes fractions
• Guess an AOD using one channel (reflectance or stokes fraction) using different aerosol models and a priori surface
• Check reliability:
Sto
kes
frac
tio
n
PM
D
refl
ecta
nce
AOD AOD
EUMETSAT METEOROLOGICAL SATELLITE CONFERENCE15/09/2013 – 20/09/2013, VIENNA
PMAp results: Aerosol Optical Depth (23/05/2011)
EUMETSAT METEOROLOGICAL SATELLITE CONFERENCE15/09/2013 – 20/09/2013, VIENNA
PMAp results: AOD clear sky cases (23/05/2011)
EUMETSAT METEOROLOGICAL SATELLITE CONFERENCE15/09/2013 – 20/09/2013, VIENNA
Verification of PMAp: Comparison to MODIS
Overpass difference: 1.0h MODIS / Terra and METOP
Main retrieval R = 0.89
AO
D (
MO
DIS
)
AOD (PMAp)
Alternate retrieval R = 0.83
AO
D (
MO
DIS
)
AOD (PMAp)
AOD (PMAp)
Cloudy pixels R = 0.71
EUMETSAT METEOROLOGICAL SATELLITE CONFERENCE15/09/2013 – 20/09/2013, VIENNA
PMAp: Cloud products
PMAp: cloud fraction PMAp: cloud optical depth
FRESCO (www.temis.nl)
Effective cloud fraction
EUMETSAT METEOROLOGICAL SATELLITE CONFERENCE15/09/2013 – 20/09/2013, VIENNA
PMAp tandem operations: AOD Metop A & Metop B
Very good consistency between METOP A & B
EUMETSAT METEOROLOGICAL SATELLITE CONFERENCE15/09/2013 – 20/09/2013, VIENNA
Looking forward: Algorithms in development
• Extension of the AOD retrieval to pixels over land (preliminary land retrieval available on prototype level)• AOD interpolation for different aerosol types at 460nm• AOD type selection using different aerosol indices between 370-
460nm• Corrections for partly cloudy pixels combining GOME and
AVHRR around 630nm
• A dedicated volcanic ash retrieval is currently being developed using the same framework:• Temperature differences & NDVI (AVHRR)• Shape of the IASI spectra (e.g. concept of Lieven Clarisse)• GOME-2 UV ratio
EUMETSAT METEOROLOGICAL SATELLITE CONFERENCE15/09/2013 – 20/09/2013, VIENNA
PMAp AOD over land: first results (30/08/2013)
EUMETSAT METEOROLOGICAL SATELLITE CONFERENCE15/09/2013 – 20/09/2013, VIENNA
Conclusions
• A new aerosol product over ocean from METOP instruments (PMAp) will be provided to users (operational in Q1/2014)
• The aerosol product is developed using a multi-instrument approach combining GOME, AVHRR and IASI
• AOD will be retrieved for clear-sky and partly cloudy scenes
• Cloud fraction, cloud optical depth and limited information on aerosol type like volcanic ash is provided in addition
• Verifications of the algorithms show promising results
• The second generation will provide AOD over land and an improved multi-sensor retrieval of volcanic ash